To provide a perform of a bioabsorptive polymer which is molecular- oriented in at least uniaxial direction suitable for formation of medical apparatus and is subjected to thermoforming treatment.

This preform is formed of the bioabsorptive polymer sheet material which is heat treated and is subjected to forming treatment by three- dimensional forming molds, by which molecular orientation is imparted to the polymer sheet material. Further, the sheet material is subjected to cooling treatment, by which its orientation is at least partly maintained.